Aqueous dispersions containing organopolysiloxanes in which at least 80 mol percent of the siloxane units are dihydrocarbon siloxane units, a filler and a dispersant, which may be used as antifoams are described in U.S. Pat. No. 3,650,979 to Steinbach et al. These aqueous dispersions are prepared by emulsifying in water an .alpha.,W-bis-(trimethysiloxy)-polydimethylsiloxane, finely divided silica, an emulsifier consisting of a polyglycol ether or a fatty acid ester thereof or an alkyl- or aryl-sulfate or -sulfonate and thereafter admixing the emulsion thus obtained with a fatty acid ester of hydroxyethanesulfonic acid or an alkali metal salt thereof.
In contrast to the antifoams prepared in the form of aqueous dispersions, self-emulsifying antifoams have the advantage that they can be stored in concentrated form. Moreover, compared to the self-emulsified antifoams known heretofore, which contain an organopolysiloxane in which at least 80 mol percent of the siloxane units are dihydrocarbon siloxane units, a filler and a dispersant, the self-emulsifying antifoams of this invention are more stable under storage conditions, i.e., they do not separate, especially when stored at elevated temperatures. Furthermore, aqueous dispersions prepared from the self-emulsifying antifoams of this invention are more stable.
Therefore, it is an object of this invention to provide self-emulsifying antifoams having improved storage stability. Another object of this invention is to provide self-emulsifying antifoams which are stable at elevated temperatures. A further object of this invention is to provide self-emulsifying antifoams which will form aqueous dispersions having improved stability.